Lightweight armor for ballistic protection applications, and more specifically lightweight personal armor is used to stop high and very high ballistic threats e.g. armor piercing (AP) bullets. For efficient low weight ballistic protection against high power penetration projectile, hard armor and specifically hard ceramic armor in form of monolith, plate, tiles, pellets or special shape ceramic elements is needed. Ceramic armor is typically used for personal protection, vehicles protection, ships, helicopters, and aircraft protection. In the field of personal protection ceramic monolith backed up by composite material is usually used. The ceramics are used due to their low density, high rigidity and high hardness that make them the most appropriate materials to defeat modern armor piercing projectiles. It has been found that in order to stop, i.e. prevent penetration of an AP threats at low weight, a ceramic-based composite is most suitable. A hard armor composite includes a rigid ceramic facing and a soft or laminated ballistic composite material/fabric. The composite material/fabric behind the ceramic plate serves to absorb the remaining energy of the bullet after hitting the ceramic facing and to “catch” the bullet, its fragments and the ceramic fragments. Ballistic ceramic materials with high hardness properties are the main constituents of the armor and improving the stopping power of the armor can be achieved mainly by increasing the stopping-power of the ceramics.
U.S. Pat. No. 4,613,535 teaches that monolithic plates can be formed from fibers coated with an elastomer. If a multi-hit ballistic panel is required, i.e., one that can withstand more than one hit, it cannot be attained using monolithic inserts. For this purpose, the insert is made of separate tiles connected together, as by gluing onto a substrate. A bullet hitting the target will destroy one or more tiles at a time, and the remaining tiles serve to prevent penetration along the remainder of the insert. Such inserts are shown, for example, in Israel Patent 120854, EP 488,465, and U.S. Pat. No. 4,868,040. These inserts are generally expensive to manufacture, since each tile must be abraded to the correct size and fit on the insert. In addition, the tile connection lines and junctions are weakened points from a ballistic point of view.
U.S. Pat. No. 4,760,611 discloses a bullet-proof waistcoat consisting of a plurality of square plates linked together by hinged joints. Each plate has a ceramic core enclosed in a resilient metal, i.e., an aluminum alloy.
It is well documented that confinement increases ballistic performance of ceramics. D. Sherman, J. PHYS IV FRANCE 7 1997, showed that confinement of the ceramics is capable of generating high compression stresses that act to reduce the damage to the ceramics and hence improve the ballistic performance of the insert. Clamping the ceramics into a confinement frame and hence arresting of the ceramics induces mechanical compression stress into the ceramics and reduces significantly their damage. T. J. Holmquist, International Journal of Impact Engineering, November 2003, evaluated the response of ceramic targets with and without pre-stress subjected to projectile impact. In all cases pre-stressing the ceramics enhanced the ballistic performance, because the ceramic strength increases as the confining pressure increases. In either case, the results demonstrate that the ballistic performance of confined ceramic targets can be improved by pre-stressing the ceramic and that the pre-stressing phenomenon can be complex.
U.S. Pat. No. 6,389,594 discloses an antiballistic article including a monolithic ceramic plate, an antiballistic backing material affixed to the ceramic monolith, and an outer shell, formed of an antiballistic material including a curable resin, enclosing the backing and ceramic monolith.
This patent teaches that in order for a monolithic ceramic to possess multi-hit capabilities these ceramics must be arrested. This is accomplished by applying iso-static force on monolith ceramics wrapped in a composite materials impregnated with thermosetting and thermoplastic composite. Upon cooling under iso-static pressure the ceramics is arrested and more shots can be stopped on the same plate. As seen above, applying internal stress and compressing the ceramic monolith is known to increase its ballistic capabilities.
GB Pat. 1352418 discloses antiballistic articles against high speed particles by means of mouldings built up from alternating layers of sintered alumina (aluminum oxide) and metals firmly bonded to one another with inorganic bonding means such as by welding, soldering or with inorganic cements. This can be done only at very high temperatures above 500° C. and up to 1200° C. Furthermore, this patent is directed to brick-shaped blocks, which are massive and heavy blocks designed to protect walls, fortress installations, and gun sites . . . particularly . . . boats, aircraft and armored cars.
It is an object of the present invention to provide improved pre-compressed ceramic-based anti-ballistic articles.
A further object of the invention is to provide a thin light weight pre-stressed ceramic article for personal use.
Another object is to provide a method for stressing ceramic plates/tiles. The pre-compressed ceramic-based anti-ballistic articles according to the present invention have superior ballistic characteristics including significant reduction or elimination of the damage to the ceramic plate/tile when being hit, thus, providing armor plate with an increase in multi-hit capabilities. In addition, the pre-compressed ceramic-based anti-ballistic articles of the present invention are of relatively low weight, decreased thickness and low cost.
Further aims, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the following figures.